U.S. patent number 5,590,399 [Application Number 08/393,210] was granted by the patent office on 1996-12-31 for up-link channel assignment scheme for cellular mobile communications systems employing multi-beam antennas with beam selection.
This patent grant is currently assigned to Nextel Communications, NTT Mobile Communications Network Inc.. Invention is credited to Tadashi Matsumoto, Seiji Nishioka.
United States Patent |
5,590,399 |
Matsumoto , et al. |
December 31, 1996 |
**Please see images for:
( Certificate of Correction ) ** |
Up-link channel assignment scheme for cellular mobile
communications systems employing multi-beam antennas with beam
selection
Abstract
An up-link channel assignment scheme for cellular mobile
communications systems employing multibeam antennas with beam
selection, in which a channel that is selected from among all
variable channels in the same frequency band may be assigned to
each of the antenna beams in a base station for communications.
Channel selection for a base station takes place independently of
that for other cells, such that the process is autonomous. Channel
selection is based upon an estimate of the signal-to-interference
power ration ("SIR") in which a channel having the smallest SIR
estimate that is larger than or equal to a given threshold value is
chosen. Alternatively, a channel having the largest SIR estimate is
selected.
Inventors: |
Matsumoto; Tadashi (Walnut
Creek, CA), Nishioka; Seiji (San Ramon, CA) |
Assignee: |
Nextel Communications
(Lafayette, CA)
NTT Mobile Communications Network Inc. (Tokyo,
JP)
|
Family
ID: |
23553745 |
Appl.
No.: |
08/393,210 |
Filed: |
February 23, 1995 |
Current U.S.
Class: |
455/449;
455/450 |
Current CPC
Class: |
H04W
16/28 (20130101); Y02D 30/70 (20200801); H04W
24/10 (20130101); H04W 28/16 (20130101); H04W
36/00 (20130101); H04W 16/10 (20130101); H04W
24/00 (20130101) |
Current International
Class: |
H04Q
7/36 (20060101); H04Q 007/30 () |
Field of
Search: |
;455/33.1,33.2,33.3,33.4,34.1,34.2,54.1,56.1,62,63 ;379/59,60
;375/348 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Sallberg et al. IEEE Hybrid channel assignment and reuse
partitioning in a cellular mobile telephone system. Jun. 1, 1987
pp. 405-411. .
Proakis, John G., Digital Communications, 2nd Ed., Chapter 4,
"Modulation and Demodulation for the Additive Gaussian Noise
Channel", pp. 220-234. .
Uddenfeldt, "The Evolution of Digital Cellular into Personal
Communications", Ericsson Radio Systems AB (Sweden), pp. 201-205.
.
Hata et al., "Radio Link Design of Cellular Land Mobile
Communication Systems", IEEE Transactions on Vehicular Technology,
vol. VT-31, No. 1, Feb. 1982. .
Mouly et al., The GSM Sysstem for Mobile Communications, 1992, pp.
600-611. .
Schwartz et al., Communication Systems and Techniques,
Inter-University Electronics Series, vol. 4, Chapter 11,
"Decision-Oriented Diversity for Digital Transmission". .
Gilhousen et al., "On the Capacity of a Cellular CDMA System," IEEE
Transactions on Vehicular Technology, vol. 40, No. 2, May
1991..
|
Primary Examiner: Eisenzopf; Reinhard J.
Assistant Examiner: Nguyen; Lee
Attorney, Agent or Firm: Glenn; Michael A.
Claims
We claim:
1. A channel assignment method for a cellular mobile communications
system having a multibeam antenna system with beam selection, the
method comprising the steps of:
estimating with said antenna a signal-to-interference power ratio
("SIR") for each channel in said cellular communications system by
measuring Euclidean distance between a desired signal and a
received signal and by averaging said measured distance over
several samples;
using said averaged Euclidean distance as a signal quality measure;
and
assigning by said antenna a communications channel to each antenna
beam of said multibeam system at a cell within said cellular system
independently of other cells within said cellular system based upon
an SIR derived value by initiating a hand-off process if said
quality measure expressed by the averaged Euclidean distance
becomes worse than a selected threshold level, selecting a hand-off
destination channel from among all available channels in frequency
band, and measuring a received composite signal power of the other
channels at a base station receiver to determine said hand-off
destination.
2. The method of claim 1, wherein said channel assignment step
selects a channel having the smallest SIR estimate that is larger
than or equal to a selected threshold value.
3. The method of claim 1, wherein said channel assignment step
selects a channel having a largest SIR estimate.
4. The method of claim 1, wherein said channel assignment step
keeps using the same channel if there are no channels having an SIR
estimate larger than a selected threshold value.
5. The method of claim 1, wherein said channel assignment step
selects any of a channel having the smallest SIR estimate that is
larger than or equal to a selected threshold value, and a channel
having a largest SIR estimate; and wherein said channel assignment
step keeps using the same channel if there are no channels having
an SIR estimate larger than said selected threshold value.
6. An up-link channel assignment apparatus for cellular mobile
communications systems employing multi-beam antenna with beam
selection, said apparatus comprising:
means for estimating with said antenna a signal-to-interference
power ratio ("SIR") for each channel in said cellular
communications system, wherein said estimating means further
comprises means for measuring Euclidean distance between a desired
signal and a received signal, means for averaging said measured
distance over several samples, and means for using said averaged
Euclidean distance as a signal quality measure; and
means for assigning by said antenna a communications channel to
each antenna beam of said multibeam system at a cell within said
cellular system independently of other cells within said cellular
system based upon an SIR derived value, wherein said assigning
means further comprises means for initiating a hand-off process if
said signal quality measure expressed by the averaged Euclidean
distance becomes worse than a selected threshold level, means for
selecting a hand-off destination channel from among all available
channels in a frequency band, and means for measuring a received
composite signal power of the other channels at a base station
receiver to determine said hand-off destination.
7. The apparatus of claim 6, wherein said channel assignment means
selects a channel having the smallest SIR estimate that is larger
than or equal to a selected threshold value.
8. The apparatus of claim 6, wherein said channel assignment means
selects a channel having a largest SIR estimate.
9. The apparatus of claim 6, wherein said channel assignment means
keeps using the same channel if there are no channels having an SIR
estimate larger than a selected threshold value.
10. The apparatus of claim 6, wherein said channel assignment means
selects any of a channel having the smallest SIR estimate that is
larger than or equal to a selected threshold value, and a channel
having a largest SIR estimate; and wherein said channel assignment
means keeps using the same channel if there are no channels having
an SIR estimate larger than said selected threshold value.
Description
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to communications systems. More particularly,
the invention relates to a channel assignment scheme for cellular
mobile communications systems employing multi-beam antennas with
beam selection.
2. Description of the Prior Art
A cellular network allows mobile communications in a specified
geographic area by dividing the area into sectors, each of which is
serviced by a cell site dedicated to that particular sector.
Cellular systems work because a low power mobile unit is passed
from cell site to cell site as the unit moves about in the service
area from sector to sector. During the passing off, the mobile unit
may be assigned a different communication frequency, known as a
channel, corresponding to the channels allocated to the cell site
in the mobile unit's current sector. In this way, the frequency
spectrum within a limited service area is reused. Thus, each
channel within the system may be used at a plurality of cell sites
simultaneously and the system can therefore support a number of
users far in excess of channels and frequency spectrum otherwise
available.
There are two efficiencies that express performance of cellular
communications systems: 1) power efficiency, and 2) spectrum
efficiency (see, for example M. Hata, K. Kinoshita, K. Hirade,
Radio Link Design of Cellular Land Mobile Communication Systems,
IEEE Trans. VT., vol. VT-31, pp. 25-31, 1982). Power efficiency
indicates how efficiently the transmitted power can be used for
communications. With regard to power efficiency, a better design of
the radio access scheme requires less received signal strength.
Spectrum efficiency corresponds to the system user capacity for
mobile communications systems that have a cellular configuration,
where the same frequency spectrum is reused in geographically
separated cells. A key concern with regard to spectrum efficiency
in cellular mobile communications systems is resistance to
co-channel interference (see, for example M. Mouly, M. B. Pautet,
The GSM System for Mobile Communications, published by the authors:
4, rue Louise Bruneau, F-91120 Palaiseau, France, pp. 601-611,
1992).
Various schemes have been proposed for the efficient reuse and
handling of channels for cellular communications systems. For
example, R. Alexis, Method and Apparatus For Selecting A Free
Channel In A Mobile Radio System, U.S. Pat. No. 4,783,780, 8 Nov.
1988 (a mobile radio system in which power levels in a signaling
path are measured and compared by a mobile station with an
interference threshold power level to identify duplex channels of
interfering fixed stations, such that a free duplex channel is
selected by the mobile station by excluding channels of interfering
and engaged fixed stations); V. Graziano, Antenna Array For A
Cellular RF Communications System, U.S. Pat. No. 4,128,740, 5 Dec.
1978 (an array of antennas for a cellular RF communications system
consisting of a plurality of antenna sites at which a plurality of
sectored antennas provide a plurality of communications channels,
and in which channels are allocated to optimize spectrum use, while
minimizing interference); and D. Reudink, Y. Yeh, Technique For
Efficient Spectrum Utilization In Mobile Radio Systems Using Space
Diversity, U.S. Pat. No. 4,355,411, 19 Oct. 1982 (a mobile radio
system in which a mobile station is operated on a first
communication channel when the mobile station is not experiencing
interference, and in which the mobile station is switched to a
different communications channel when an interference threshold
level is exceeded).
The use of a combined directional multibeam antenna with beam
selection is known to be effective in reducing the amount of mobile
station transmitter power required to establish and maintain an
acceptable communications path. A antenna beam exhibits sensitivity
to signals that are received from a specific direction. In such
scheme an array of beams is employed, and a beam having the largest
received signal strength is selected. Hence, the use of a multibeam
antenna system with beam selection improves power efficiency in a
communications system.
However, with regard to co-channel interference, the beam selector
may select a beam that is subject to co-channel interference if
such beam produces the largest received signal strength. Such
interfering selection is more likely to happen as the cell radius
in a cellular communications system becomes smaller.
The problem of co-channel interference can be eliminated by
decision oriented channel estimation schemes (see, for example M.
Schwartz, W. R. Benett, S. Stein, Communication Systems and
Techniques, McGraw-Hill, pp. 490-584, 1966). In such schemes, an
adaptive filter based upon the least-square error criterion is used
for channel estimation, where the Euclidean distance between the
desired and the received signals is used as an error component. A
signal having the smallest squared error is then selected from
among the signals received by the multiple beams.
Another simple beam selection scheme is based upon unique word
detection, where a unique word or pilot signal is embedded in a
transmitted symbol stream. The receiver correlates the received
signal with the unique word pattern. A signal having the largest
correlation value is then selected.
It is well understood in the art that a multibeam antenna system
that employs one of the various known beam selection schemes can
improve the spectrum efficiency. This is because it is unlikely
that the interference source is located coincidentally in the
pattern of the desired beam. However, if cellular system
communications frequencies are allocated to each beam in the
multibeam antenna system, such that the spectrum reuse distance
between each beam within the sector satisfies the system's
signal-to-interference power ratio ("SIR") requirement, then such a
multibeam antenna system with beam selection is equivalent to a
sectored cell configuration. Accordingly, no advantageous outcome
over the sectored cell would result from beam selection.
It would be advantageous to provide an improved beam selection
scheme for a multibeam antenna system, such that beam selection
improves power and spectrum efficiencies in a cellular
communications system.
SUMMARY OF THE INVENTION
The invention provides an improved channel assignment scheme for
cellular mobile communications systems, including an efficient
up-link channel assignment scheme for multibeam antenna systems
with beam selection. The channel assignment scheme improves the
spectrum efficiency of the cellular communications system over that
provided by a sectored cell configuration. In the invention,
channels are not allocated to each individual beam of the multibeam
antenna system. Rather, each beam can use all of the available
channels in the same frequency band. The SIR is determined for each
channel. The channel having the smallest SIR estimate larger than
or equal to a given threshold value is selected, and that channel
is assigned to each of the antenna beams in base station for
communications. Alternatively, a channel having the largest SIR
estimate is selected. This process takes place independently of
other cells within the cellular system.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of an ideal hexagonal cell
layout for a cellular mobile communications system;
FIG. 2 is a schematic representation of an approximation of an
antenna beam pattern;
FIG. 3 is a schematic representation showing antenna beam patterns
in which each base station provides a different directivity, such
that all directions are covered;
FIG. 4 is a graph plotting the outage probabilities versus the
number K of per-cell users, where the number of channels N=32 and
number of beams B=6, showing perfect sensitivity isolation (G.sub.a
=-.infin.dB) for random channel assignment and for autonomous
channel assignment with two algorithms ("A" and "B") according to
the invention;
FIG. 5 is a graph plotting the outage probabilities versus the
number K of per-cell users, where the number of channels N=32 and
number of beams B=6, showing a sensitivity isolation (G.sub.a =-20
dB) for random channel assignment and for autonomous channel
assignment with two algorithms ("A" and "B") according to the
invention;
FIG. 6 is a graph plotting the outage probabilities versus the
number K of per-cell users, where the number of channels N=32 and
number of beams B=6, showing a sensitivity isolation (G.sub.a =-10
dB) for random channel assignment and for autonomous channel
assignment with two algorithms ("A" and "B") according to the
invention;
FIG. 7 is a graph plotting the outage probabilities versus the
number of beams for a first autonomous channel algorithm ("A")
according to the invention; and
FIG. 8 is a block schematic diagram of a base station configuration
according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
The invention provides an efficient up-link channel assignment
scheme for multibeam antenna systems with beam selection. The
scheme described herein improves the spectrum efficiency of a
cellular communications system over that of a sectored cell
configuration. The scheme does not allocate frequencies
individually to each beam. Rather, each beam can use all the
available channels in the same frequency band. The
signal-to-interference power ratio ("SIR") is estimated for each
channel. The channel having the smallest SIR estimate larger than
or equal to a given threshold value is selected, and assigned to
each of the antenna beams in base stations for communications. This
process takes place independently of other cells.
FIG. 1 is a schematic representation of an ideal hexagonal cell
layout for a cellular mobile communications system. The system
shown in the figure consists of 19 cells, although the invention is
applicable to any size system. The base station antenna in the
system has B beam antennas (see FIG. 3). The beam pattern is
approximated, as shown in FIG. 2. FIG. 2 also shows the sensitivity
spillover factor G.sub.a. For purposes of the discussion herein,
the sensitivity spillover factor is identical with the sensitivity
isolation factor (or the sensitivity isolation ratio). The
sensitivity spillover factor is caused by side robes of the antenna
pattern. It may be assumed that for computational simplicity, the
antenna pattern can be approximated by that shown in the figure,
which is an approximation of the worst case.
FIG. 3 is a schematic representation showing antenna beam patterns
for three base stations, in which each base station has a different
directivity (i.e. B=2, B=3, and B=6), such that all signal
directions within the base station sector are covered. Every beam
has a sufficient number of receivers that are adapted receive
signals of all the available channels, such that full sector
coverage is provided. A beam that is oriented to cover an area in
which a desired reference user is located is selected from among
the B beams using a decision oriented channel estimation scheme.
The Euclidean distance, i.e. the distance between the two signal
points defined in the modulation format (see J. G. Proaki, Digital
Communications, pp. 220-234, McGraw-Hill Book Company), between the
desired signal point and the received signal point is measured, and
then averaged over several symbols.
The Euclidean distance can be measured as follows: symbol decision
on the i th received signal complex envelope z.sub.i is made by a
decision circuit f(*). The Euclidean distance between the desired
signal and the received signal points is then calculated as
.vertline.f(z.sub.i)-z.sub.i .vertline.. The averaging process for
the Euclidean distance is formulated as: ##EQU1## where N is the
averaging length.
The averaged Euclidean distance is then used as a signal quality
measure.
The j-th base station's (for example, refer to FIGS. 1 and 2) k-th
beam receiver receives signals transmitted from the i-th mobile
station with the power of:
where rij is the distance between the i-th user and the j-th base
stations, .rho. is the distance attenuation factor, and .eta. is a
random variable corresponding to shadowing which is log-normally
distributed with a mean of 0 dB, and with a standard deviation of
.sigma..sub.5 dB. Without loss of generality, it has been assumed
for purposes of this example of the invention that the transmitter
power is unity.
There are N channels in a cellular communications system. For
simplicity in explanation, frequency division multiple access
("FDMA") is assumed, where different frequencies are assigned to
the channels. However, as with time division multiple access
("TDMA") systems, several of the channels can use the same
frequency at different time slots. It will be apparent to those
skilled in the art that the invention is readily applied to TDMA
systems, where the "SIR" is used as a signal-to-interference power
ratio in a time slot of interest.
Each beam can use all of the available channels in the same
frequency band. In this example, the i-th user communicates with
the j-th base station's k-th beam. Assume that there are M users
including the i-th user in the entire coverage who use the l-th
channel. The received signal-to-interference power ratio,
SIR.sub.i, for the i-th user can then be expressed as: ##EQU2##
m.di-elect cons.users in the l-th channel, m.noteq.i.
The base station receiver also knows the P.sub.ijk value, for
example P.sub.ijk can be measured by using frequencies assigned to
control channels. See M. Mouly, M. B. Pautet, The GSM System for
Mobile Communications, published by the authors, pp. 616-620,
1992). If the quality measure, as expressed by the averaged
Euclidean distance, becomes worse than a threshold level, then a
hand-off process is initiated. The hand-off destination channel is
selected from among all the available channels in the frequency
band. To determine the hand-off destination, the base station
receiver measures the received composite signal power P.sub.L, of
the all other available channels, where:
m.di-elect cons.users in the L-th channel.
As shown in Equations (4) and (5), the P.sub.ijk /P.sub.L value can
be used as an estimate of the L-th channel's SIR. An algorithm,
e.g. algorithm A or B, is used to determine the hand-off
destination channel, where:
If there are no channels having an SIR estimate larger than the
threshold value, then the i-th user keeps using the same channel.
However, this user's communications quality is not necessarily
worse than that guaranteed by the threshold SIR. The channel
assignment process takes place in each cell simultaneously and
independently of that of other cells, and therefore a better SIR
may result even though the i-th user stays in the same channel.
Computer simulations were performed to evaluate the outage
probability when algorithms A and B are used. The process herein is
simulated as follows:
Assuming that users are uniformly distributed within an entire
service area, the i-th user's location is determined as a
two-dimensional uniformly distributed random variable with a range
covering all areas considered. A hexagonal cell layout with three
rings, as shown in FIG. 1, is considered. In the example, there are
19 cells in the entire service area (see FIG. 1). K users are first
located over each of the 19 cells.
For each user location, a log-normally distributed random variable
10.sup..eta./10 with a standard deviation of .sigma..sub.s, which
represents shadowing, is generated and multiplied by
r.sub.ij.sup.-P, which represents distance attenuation. In mobile
communications environments, the average signal strength received
by a mobile station, of which the distance from the base station is
r, can be expressed by Eq. 1 above. Furthermore, if the mobile
station is out of the antenna beam pattern, the antenna sensitivity
spillover factor G.sub.a is multiplied by r.sub.ij.sup.-P
10.sup..eta./10 to express the antenna's directivity.
This process is repeated for all the i, j, and k values, where
1.ltoreq.i.ltoreq.K, 1.ltoreq.j.ltoreq.19, and 1.ltoreq.k.ltoreq.B.
A beam having the largest received signal power is then selected
for each user to determine the base station and antenna with which
the user communicates. After this process, some cells may
accommodate more than K users, and some other cells may have less
than or equal to K users. Each base station selects channels
randomly from among the N available channels, and assigns them to
the users that are communicating with the base station. The
received composite signal powers P.sub.L 's, 1.ltoreq.L.ltoreq.N,
are then calculated for all the beams associated with each base
station.
For all users communicating with each base station, the received
SIR's given by Eq. (3) above are calculated, and then checked to
determine if the received SIR is larger than or equal to a selected
threshold level. If not, hand-off is initiated, and the hand-off
destination channel is given using one of the channel assignment
algorithms described above. This process takes place independently
of other cells, and is repeated. The number of the users having
received SIR that were less than the threshold level were then
summed. When the number n of such users can not be further reduced,
the process is stopped. The outage probability is then given by
n/(19.times.K).
FIG. 4 is a graph plotting the outage probabilities versus the
number K of per-cell users, where the number of channels N=32 and
number of beams B=6, showing perfect sensitivity isolation (G.sub.a
=-.infin.dB) for random channel assignment and for autonomous
channel assignment with algorithms A and B according to the
invention; FIG. 5 is a graph plotting the outage probabilities
versus the number K of per-cell users, where the number of channels
N=32 and number of beams B=6, showing a sensitivity isolation
(G.sub.a =-20 dB) for random channel assignment and for autonomous
channel assignment with algorithms A and B according to the
invention; and FIG. 6 is a graph plotting the outage probabilities
versus the number K of per-cell users, where the number of channels
N=32 and number of beams B=6, showing a sensitivity isolation
(G.sub.a =-10 dB) for random channel assignment and for autonomous
channel assignment with algorithms A and B according to the
invention. In each above figure, it is assumed that .sigma..sub.5
=8 dB, .rho.=3.5, and the threshold SIR is 20 dB.
FIGS. 4, 5, and 6 plot the outage probabilities with algorithms A
and B, together with random assignment, where there is no channel
hand-off based upon SIR measurement. It can be seen that algorithm
A achieves better performance than the other two schemes. Thus,
with perfect sensitivity isolation, forty users can be accommodated
with an outage probability of 10%. This user capacity gradually
decreases as the sensitivity spillover factor increases. However,
25 users can still be accommodated even when G.sub.a =-10 dB. This
78.1% (=25/32) accommodation of per-cell capacity is unexpected,
and is much higher than recent results of Code Division Multiple
Access ("CDMA") capacity estimation (see, for example K. S.
Gilhousen, I. M. Jacobs, R. Padovani, A. J. Viterbi, L. A. Weaver,
Jr., C. E. Wheatly, On the Capacity of a Cellular CDMA System, IEEE
Trans. VT., vol. VT-40, pp. 303-312, 1991).
Outage probability with algorithm B is not as good as that with
algorithm A, but it is better than that of random assignment.
However, user capacity with algorithm B also decreases as the
sensitivity spillover factor increase. Thus, when G.sub.a =-10 dB,
the algorithm B outage probability is almost identical to that of
random assignment.
Table 1 below compares for 2% blocking probability the per MHz
Erlang capacity, i.e. the maximum number of calls that the system
can carry (see J. Uddenfeldt, The Evolution of Digital Cellular
Into Personal communications), of a Motorola Integrated Radio
System ("MIRS"), i.e. the Research & Development Center for
Radio Systems ("RCRS") of Japan standard no. 32 for digital
multiple channel access (digital "MCA"), system with an Advanced
Mobile Phone System ("AMPS") and Qualcomm's CDMA systems, Cellular
Telecommunications Industry Association ("CTIA") interim standard
no. IS95, where a 1-MHz system bandwidth is assumed. It is assumed
that B=6 and G.sub.a =-10 dB for the proposed scheme. If the
required outage probability is 10%, an MIRS system using the
invention herein can achieve 2.5 times as large an Erlang capacity
as hat provided by Qualcomm's CDMA system. If the required outage
probability is 1%, 1.4 times the Erlang capacity gain can be
achieved using the invention.
TABLE 1 ______________________________________ Relative Spectrum
Efficiencies of AMP's and Qualcomm's CDMA, Current MIRS, and MIRS's
in Accordance with Algorithm "A" of the Invention Qual- MIRS MIRS
MIRS comm (Algorithm (Algorithm System AMP (current) CDMA A) A)
______________________________________ Re-use 7 9 1 1 1 pattern (3-
(10% (1% Sector) Outage) Outage) Erlang 1 11.56 41.76 104.4 60.0
Capacity Gain ______________________________________
FIG. 7 is a graph plotting the outage probabilities versus the
number of beams for autonomous channel algorithm A according to the
invention, where N=32 and the number of per-cell users is 24, in
which the sensitivity spillover factor is used as a parameter. As
shown in the figure, a 10% outage probability can be achieved with
a 3-beam antenna with perfect isolation, and a 15% outage
probability can be achieved with G.sub.a =-20 dB.
FIG. 8 is a block schematic diagram of a base station configuration
according to the invention. In the figure, a plurality of beam
antennas 12, 13, 14 are shown. Each beam antenna is coupled to a
respective plurality of receivers 15, 16, 17. Each receiver
produces a signal indicating received signal strength at a
corresponding set of output terminals 18, 19, 20.
Each receiver operates on a particular frequency channel and
provides an output signal that indicates the average Euclidean
distance of the signal for the channel, as described above. This
output signal is coupled via a terminal 21, 22, 23 to a beam
selector 24, 25, 26 for each channel. The output of the beam
selector is the averaged Euclidean distance for the selected beam
and is coupled, e.g. via line 36, to a monitor/hand-off initiator
27, 28, 29. Thus, the beam selector for channel 1 (24) receives a
signal indicating averaged Euclidean distance for channel 1, and so
on.
The monitor/hand-off initiator is in turn coupled to an control
module 30, 31, 32 that implements one of the algorithms described
above, e.g. algorithm A or B, and that also has inputs 33, 34, 35
that are coupled to receive the various received signal strength
signals ("RSSi") 18, 19, 20.
Although the invention is described herein with reference to the
preferred embodiment, one skilled in the art will readily
appreciate that other applications may be substituted for those set
forth herein without departing from the spirit and scope of the
present invention. For example, the two channel assignment
algorithms described herein are provided for purposes of example
only. It is expected that the invention will find ready application
with other desired algorithms. Accordingly, the invention should
only be limited by the claims included below.
* * * * *